This work presents the application of graphene oxide (GO) thin films, which are prepared on indium tin oxide (ITO) electrodes by solution spin coating method, as the hole transport layer in organic photovoltaics (OPVs). The thickness of GO films is optimized by adjusting the spin speed, and the effect of GO thickness on the performance of solar cells is investigated. Based on this, the performance of solar cell devices is further improved by using such methods as ultraviolet ozone (UVO) and annealing treatments. The results show that when the temperature of UVO and annealing treatments reach 250 ℃, the OPV devices achieve the highest power conversion efficiency of 3.16%, which is close to the result using a classical poly (3,4-ethylenedioxythiophene): polystyrene sulfonic acid (PEDOT: PSS) material. This result has indicated that GO, with such advantages as low-cost, solution processing, and excellent light transmittance, will become a promising and effective material for hole transport layer in OPVs.